Southernmost Marathon & Half Marathon

October 12, Key West, FL

Missing summer already? Head south—way south—on Columbus Day weekend to the inaugural "SoMo Marathon."The Key West-based race promises "no hills and no chills," and both the half and full courses offer miles of ocean and gulf views. (The marathon takes you off of the island and up to historic U.S. Route 1's Mile Marker 9 for the turnaround.) After the race, party with live music and awards at Pat Croce's Rum Barrel Bar & Grill, and enjoy discounts and festivities around the island all weekend. Online registration closes October 5. Fee: $85 - $110.

Peak Season Century Ride

October 12, Lake George, New York

If you'd rather ride than run your way into fall, consider a century ride in the beautiful northeast. The Peak Season Century, around historic Lake George and through the Adirondacks in upstate New York, offers 60- and 100-mile options packed with rolling hills, gorgeous autumn foliage, and plenty of rest stops, food and bike mechanics along the way. A limited number of day-of registrations will be available. Fee: $100.

NYC Cupcake Run 5K

October 19, Astoria, New York

For those who can't wait until the victory party to celebrate with something sweet and sugary, there's New York City's first annual Cupcake Run. This 5K, which includes three checkpoints where runners eat one cupcake each, will take place in Astoria Park in the borough of Queens, and participants can wash down their cupcakes with a free drink at a local bar after the race. A portion of the proceeds will be donated to the volunteer service organization New York Cares. Registration opens September 20 and is expected to sell out before race day. Fee: $45.

Mustache Dache 5K Series

November, Various locations and dates

Men, women and children are invited to "embrace their inner Mario or Luigi" in this eight-city 5K series whose proceeds benefit Movember, a global men's health charity fighting prostate and testicular cancer. While the guys are invited to grow their own 'staches for the run, ladies are encouraged to don fake facial hair or take advantage of on-site face painters before the race. At the after-party, participants can visit a photo booth, enter a costume contest, or refuel with goodies from local food trucks. Registration for all races ends October 13. Fee: $35 - $40.

Mermaid Run 5K, 10K and Sirena 10

November 10, San Francisco, CA

Run the Golden Gate Bridge in the Mermaid Run's new Sirena 10-mile option, or opt for the two shorter courses that still offer breathtaking views of San Francisco Bay, the bridge and the city skyline. All Mermaid Series events are open to women of all abilities, and provide training and motivation through an active online community. (Check out their website for more runs, triathlons and duathlons across the country in 2014.) Online registration for the San Francisco run closes November 7, but you might want to sign up ASAP: The event has sold out for the past three years! Fee: $50 - $85.

Spartan Race Series

Various dates and locations

Of all the obstacle-course mud runs out there, the Spartan Race may offer the most options for athletes of all levels: a 3-mile Sprint course, an 8-mile Super Spartan and a 12-mile (or more) Beast event. Plus, they're all over the country, with upcoming 2013 races in Wisconsin, Nebraska, South Carolina, Mississippi and Boston, to name just a few. Intimidated by all that fire, water and barbed wire? Keep in mind that women make up more than a third of Spartan participants—and we've got your back with the perfect training plan and race-day checklist. Fee: $73 to $205.

Rock N Roll Las Vegas Marathon, Half & "1/2 of the Half"

November 17, Las Vegas, NV

The Rock 'n' Roll Marathon Series is known for putting on great parties, and its annual Las Vegas event may be the biggest one of the year, drawing more than 32,000 runners to Sin City's famous Strip. In 2013, runners can choose from a full, half, or "1/2 of the half" (6.5 miles) course, all of which include access to a pre-race concert, bands along the course and plenty of post-race parties. Registration closes November 10, if it doesn't sell out first. Fee: $165 - $180 ($80 - 90 for 1/2 of the Half).

Brazen New Year's Eve Half Marathon

December 28, Castro Valley, CA

Close out your year on the right foot with this Bay-Area trail run that takes place on the last Saturday in December. Runners can choose from a 5K, 10K, or half marathon course—and the truly ambitious can opt to run the entire "Brazen New Year Marathon," which consists of 13.1 miles on December 28 and 13.1 miles (same course, reverse direction) on January 1. (Then, the race organizers say, you can brag to your friends: "It took me two years to finish that marathon!") A "Hiker's Start" is offered an hour early to participants who plan to walk the half marathon and take longer to complete the course. Morning-of registration will be available if the race hasn't been sold out, but shirts are only guaranteed to those who sign up by December 15. Fee: $34 - $65.